Transfer cases are used in vehicle drive lines, specifically full and part-time four-wheel drive vehicles to transfer power received through an input shaft typically from the vehicle transmission, to a pair of output shafts. One of the output shafts powering the front drive wheels and the other output shaft powering the rear drive wheels.
The transfer case is typically equipped with a speed or gear reduction unit for providing high-range and low-range operation. The transfer case may also incorporate additional drive or operation modes such as neutral, for disengaging the transmission from the front and rear axle for towing, and a locked position, for distributing power to both the front and rear axles to control wheel slippage with respect to the front and rear axles. Full-time or All-wheel-drive transfer cases include some type of differential unit to allow a speed variation between the front and rear axles.
In order to achieve the various drive or operation modes, transfer cases often incorporate a planetary gear set. Typically, a transfer case utilizes two separate planetary gear sets, one that functions as a reduction gear set and the second that functions as a differential gear set.
There is, however, a need to reduce the overall package size of the transfer case to provide a more compact design and enable the transfer case to fit in a smaller area. Several attempts have been made at incorporating or combining the functions of both the reduction planetary gear set and differential gear sets in the same package. While such attempts may result in a reduction in overall package size, there still remains a need for a transfer case that combines the functions of both the reduction and differential gear sets in the same device to while reducing overall part use and the corresponding size of the assembly.